I had the chance to work with a very experienced team with regards to building a new company. You get more responsibilities than you would in corporate settings. It's a great environment to develop in and be guided by experienced entrepreneurs.
Cons
Just like in most startups not all processes, responsibilities etc. are always clear. For people who need a lot of structure this might be a disadvantage but on the other side of the medal its a big opportunity to assume responsibility and establish new ideas.